The present invention relates to printing hammer assemblies for high speed line printers which utilize a fast moving, steel character band and high speed hammer assemblies for hitting the band at the location of the appropriate characters on the band to print upon the band and especially to a combination of techniques for improving the operation and speed of the hammer assembly.
In the impact printing field, a wide variety of printing techniques have been used in the past including those employed in the ubiquitous typewriter: the drum printer, the wheel printer, and the chain or belt printer. In the present type of printer, an endless, steel character band having various characters of the alphabet as well as numbers embossed or raised upon the band, is rotated between a drive pulley and an idler pulley. As the band is driven at high speeds adjacent a platen, a bank of parallel hammers is driven at a high speed at the moment the particular desired character is passing on the band to print the character upon the paper. The print hammer actuators are typically electromagnetically actuated, such as by solenoids, which magnets are energized by the driving circuit with each pass of the character band. The hammer assemblies need to be spaced close to each other so that a large bank of hammers can fire as the band is passing; and each hammer must respond rapidly in view of the fast moving band which might otherwise smear the character if the hammer were operating at too slow a speed. Accordingly, the present invention is directed towards a hammer assembly of a high speed printer designed for increasing the speed of the actuators with an increased speed of the character band. To accomplish this, a number of techniques have been utilized to produce a printer that can print in excess of 2000 lines per minute with a 48 character set.
In the past, a variety of print hammer assemblies for high speed printers have been provided, and some of these may be seen in the following U.S. Pat. Nos. 3,144,821, to Drejza; 3,719,139, to Niccolai; 3,289,575, to Wassermann; 3,285,164, to Makavazos; 3,584,574, to Smith; 3,726,213, to Herbert; 3,707,122, to Cargill; 3,285,166, to Helms; 3,745,495, to Chai; 3,748,613, to Venker; 3,314,359, to Martin; 3,166,010, to Fradkin; 3,734,013, to Belser; 3,172,352, to Helms; 3,449,639, to Brown; 3,592,311, to Chou; 3,656,425, to Albo; 3,460,469, to Brown; 3,659,238, to Griffing; 3,630,142, to Fulks; and 3,502,190, to Smith.
In addition to these assemblies, one U.S. Pat. No. 3,285,165, to Richter, teaches a print hammer control apparatus for a high speed printer in which a plurality of print hammer actuators respond to a signal applied thereto for energizing adjacently flanking pairs of actuators with signals of substantially the opposite polarity. In this patent, each magnet has a pair of windings as in a typical hammer actuator format and cross-talk between adjacent print hammer actuators is controlled by the application of a field of opposite polarity adjacent each magnet. This is accomplished in one case by auxillary coils located between the hammer assemblies and in a second embodiment utilizing NRC circuit connection, connecting adjacent coils of opposite polarity. The present invention advantageously handles cross-talk by the placing of two magnets adjacent a striker with only one coil per magnet in the striker assembly, and thereafter having one of the magnets in each assembly of opposite polarity from the adjacent magnet while maintaining the second magnet of the same polarity in adjacent hammer assemblies, so that like magnets have cross-talk while unlike magnets of adjacent hammer assemblies have cross-talk substractive and effect a cancellation by equal amounts of additive and substractive cross-talk.